Introduction
In our TB-scale production system, a few queries had MAXDOP 4 hardcoded into them. The goal was to improve reporting performance. Instead, CPU usage spiked and the entire server slowed down—even simple queries were affected.
This article explains how MAXDOP works, what SQL Server considers when deciding to use parallelism, and why the wrong setting can hurt more than help. We’ll walk through real tests, show what happens under load, and explore how tuning parallelism without understanding it can cause serious problems.
What Went Wrong: MAXDOP Misuse in Production
We found that application developers had started adding